Dear Forum,
I have posted this just in case it helps someone, somewhere, some time.....
I had succeeded in getting my LTFT's to balance out at a consistent 6.25% for both banks. I have read (somewhere on here) that ideally they should be around about up to 5% (either way), so I decided to have one more good look around my vacuums. Obviously, if there was a problem, it must be between the MAF Sensor and the inlet manifold, because both banks are identically a little lean? (please correct me if I am wrong). Anyway, to cut to the chase, I found that the 'Resonator' (That sort of rectangular thingy attached to the large flexible pipe from Air box to Throttle Body) was cracked along it's seam, such that I could blow air through the seam into the box.
Both LTFT's consistently under 5% now!

 

Good find.